Entergy spokesman Terry Young says the leak was caused when sparks from welding work damaged a tarp separating the leaky tank that’s under repair from the control room below.

“Total leakage into the control room was less than four tablespoons of water,” Young said. “Now with that said, no water intrusion is acceptable to us. But I just want to emphasize that this posed absolutely no threat to safety of personnel or equipment.”

Federal regulators could not confirm the amount of the leakage, beyond “three drops per minute, for less than 24 hours.” Young says the water came from nozzles that are attached to the tank. The tank was drained, and the nozzles capped, but he says the water likely came from one of those nozzles.

“After last year’s leak into the control room the company put a tarp and catch trays in the catacombs,” Nuclear Regulatory Commission spokeswoman Viktoria Mitlyng said.

The tank sits on the roof, below the roof are catacombs and below those is the control room’s ceiling.

“They cannot start up without finding and fixing whatever caused the leak into the control room,” Mitlyng said. She says the NRC has six specialists on site, in addition to the two resident inspectors.

Kevin Kamps of Beyond Nuclear says he asked about the former leaks into the control room as recently as last month. “I was told by company and agency spokespeople that that issue was a thing of the past, that an installed moisture barrier had taken care of the problem,” Kamps said in a written statement.

“If Palisades can’t even prevent basic leakage through the ceiling of the control room, which has now been going on for over two years, what does that say about its reactor and radioactive waste safeguards?”

Young says a new “spill barrier” is on site. He couldn’t say immediately if the company considered it a permanent fix.

During repairs, the company realized the flooring beneath the tank was not built as drawings indicated. Specifically, a sand bed the tank was supposedly resting on did not exist. The company had assumed that low level leakage after the tank was repaired last summer was due in part to the sand bed being wet.

“It was impossible to say where those very low levels of leaks were coming from because there were no detectable flaws (in the tank) through any of the examinations,” Mitlyng said. She says the leak had not stopped after the repairs last year, but that the rate was low enough it wasn’t against regulations.

The tank is original construction, so Young points out the lack of a sand bed was done decades ago by a different company. Entergy bought Palisades in 2007 from Consumers Energy.

“At the time the decision was made not to put sand under there, they also did not update the drawings,” Young said. “So we assumed it was there. It turns out that is wasn’t. But what we put in place now is even vastly superior to what that sand would have done.”

The new sub-flooring will consist of a fiber board with reinforced concrete.

Repairs of the leaky tank continue. Young says workers are expected to finish the partial replacement of the tank bottom this week and begin a series of tests to confirm the tank is fixed. Young expects the plant will likely restart in early summer.

COVERT TOWNSHIP, Mich. (AP) - Operators of the idled Palisades Nuclear Power Plant in southwestern Michigan say repairs to a tank that leaked slightly radioactive water into Lake Michigan will take until early summer to complete.

The plant is in Van Buren County's Covert Township, about 80 miles east-northeast of Chicago,

Congressman Fred Upton (MI-06) will head to southwest Michigan this afternoon, to check out the condition of the Palisades Nuclear Power Plant.

The unplanned release of slightly radioactive water into Lake Michigan earlier this month “outraged” the Republican congressman, who chairs the U.S. House’s Energy and Commerce Committee.

“Every option must be on the table to ensure that the continuing leak will not occur again,” Upton said in a statement last week, suggesting that a full replacement of the leaky water tank may be in order.

Officials from the nuclear plant maintain that the leak will not harm the public or any of the plant’s 650 workers.

A commissioner from the Nuclear Regulatory Commission will be accompanying Upton on his tour today.

The congressman is expected to speak publicly after the visit.

Michigan Radio's Lindsey Smith will be there and she'll bring us more later today.

You can listen to a related Environment Report segment above or read an expanded version below.

Even though Palisades is temporarily shut down, the nuclear power plant last night held a public open house it had scheduled more than a month ago.

In a small conference center in South Haven Tuesday night, anti-nuclear activists mingled with federal nuclear regulators, residents, and plant workers. Palisades Site Vice President Tony Vitale says that's a good thing. He says the open house is designed for people in the community to come talk to some of the plant workers firsthand.

“We’re not hiding anything. We want to run, and will run, and I will demand we run a transparent operation,” Vitale said.

Upton is demanding accountability and a permanent fix to the tank, which has leaked on and off for at least two years.

In a written statement, Upton says he plans to personally visit the site with a Nuclear Regulatory Commissioner.

“It is my understanding that the water tank will be emptied by the end of the week with the hope that the cause of the leak can be identified shortly thereafter. Every option must be on the table – including a full replacement of the tank – to ensure that the continuing leak will not occur again,” Upton said.

Requests for an interview were not immediately returned.

New documents show Entergy had asked regulators for an alternative fix for the leaky tank on April 25th. Those documents assumed the leaks had stabilized.

“The current leak rate is stable without an increasing trend which suggests that the current through wall flaws have self-relieved the initiating stresses, are not growing, and remain well below the calculated allowable flaw length.”

The Nuclear Regulatory Commission is investigating why the leak rate went from one gallon per day late last week to 90 gallons a day in one 24-hour period.

In the documents, Entergy requests an alternative fix for the tank “that would add a fiberglass-reinforced vinyl ester liner to the tank bottom and to a portion of the tank wall in lieu of identifying the location of the thru-wallleak(s) and performing code compliant repairs.”

During an online public meeting Tuesday night, federal nuclear regulators reiterated their belief that the Palisades nuclear power plant in Covert, Michigan, near South Haven is safe.

The Nuclear Regulatory Commission hosted the meeting to talk with the public about the strength of the vessel that contains the nuclear reactor and fuel. Radiation, high pressure and temperatures over long periods of time make the metal vessels in all pressurized water reactors more vulnerable at nuclear plants.

Palisades is the oldest nuclear power plant in the state, and it’s got one of the most brittle reactor vessels in the country. Older nuclear plants like Palisades have some copper in the mostly steel vessel; later designs have stronger steel, regulators said.

Mark Kirk is a Senior Materials Engineer in the Office of Nuclear Regulatory Research at the NRC.

“It’s unquestionably true that Palisades, one of the welds in Palisades, is one of the most embrittled in all of the plants operating in the US,” Kirk said. “Even so, Palisades continues to operate in compliance with the relevant NRC rules.”

By 2017 the plant’s vessel will become too brittle to legally operate.

This year federal regulators will keep a close eye on the Palisades Nuclear Power Plant. The plant had three safety violations last year; that makes it one of only four nuclear plants in the nation with such a bad safety rating.

About 700 people work at Palisades every day. It’s one of (if not) the largest employers in Van Buren County. The plant is the county’s largest taxpayer. Those tax dollars go to a number of public schools, libraries, a hospital and local governments.

People who live by the plant near South Haven (Covert Township) are still trying to figure out what the safety violations mean to them. It’s making others, like Barbara Geisler and her husband Maynard Kauffman, uncomfortable.

This story has been modified to correct a metric conversion and the reference to the substance tritium.

The Palisades plant near South Haven has an aluminum water tank that’s used in case of emergencies or when the plant needs to be refueled. Last month, Entergy, the company that owns the plant, shut the reactor down to fix a leak in the tank.

Palisades knew the tank was leaking for longer than the company first said

It appears that the water tank has been leaking for a lot longer than the company first admitted.

Crews are still trying to figure out exactly what caused an unplanned release of slightly radioactive water from the Palisades Nuclear Plant last week. They have discovered a new crack in a water tank that’s been leaking on and off for at least two years.

The Palisades nuclear power plant is returning to service after being shut down for the last four weeks to repair a leaking water tank.

The tank is a giant aluminum sphere that holds 300,000 gallons of water in case of emergencies or a planned refueling outage.

The tank is made up of a bunch of aluminum plates welded together. There are 26 plates on the bottom of the tank. Palisades spokesman Mark Savage says they found “several minor through wall leaks” in the aluminum walls and some flaws in the welds themselves and repaired them all.

“The most important thing to understand regarding this shutdown is the health and safety of our employees and the public has never been impacted by this issue,” said Terry Young, Vice President of Nuclear Communications for Entergy.

He confirms the unplanned release of slightly radioactive water into Lake Michigan, but couldn’t say exactly how much.

“It’s really impossible to tell at this juncture what the length of this shutdown will be because we haven’t yet had a chance to identify what the issue is that we’re going to need to fix,” Young said.

This will be the third attempt to fix the leaky tank within the last year and a half.

“We have gone through pretty exhaustive measures on a couple of occasions to bring the plant offline and do just extensive testing and repairs and we’ll take a look at what’s causing the leak this time,” Young said.

I asked if it would make more sense to replace the tank instead.

“I really don’t know any background information on that in terms of what that would cost, I honestly couldn’t comment on that,” Young said.

Young notes the plant has had “a lot of success” at Palisades in the year and a half in “significantly improving performance.” The NRC recently upgraded the plant's safety rating after a series of problems in 2011 left it with one of the worst safety performance ratings in the country.

Last month Site Vice President Tony Vitale noted that a number of issues “have required repairs to be done with the plant offline and that’s unacceptable.” He says they’re reviewing their procedures to see if there’s something they should change.

“We’re diving into our programs and finding out why these issues are finding us instead of us finding them,” Vitale said in April.

“It is unfortunate that this is a recurrent issue that we are dealing with here,” Young said, “but our resolve is strong to fix this issue once and for all.”

Updated 1:11 p.m.

Officials from the Nuclear Regulatory Commission estimate 79 gallons of "slightly" radioactive water drained into Lake Michigan on Saturday.

NRC Spokeswoman Viktoria Mitlyng says the agency doesn’t know exactly how radioactive the water was, but based on general knowledge of where the water came from, there is no risk to public safety.

“The unplanned release of this radioactive water is not something you want to have happen,” Mitlyng added.

The water came from a large water tank on the roof of the Palisades plant’s control room. It holds 300,000 gallons of water in case of emergencies or a planned refueling outage.

The plant is located in Covert Township, about 70 miles southwest of Grand Rapids.